1. Field of the Invention
This invention relates to the treatment of seizure disorders and, and more particularly relates to techniques for warning patients of an epileptic seizure.
2. Description of Related Art
Epilepsy is a condition characterized by recurrent seizures which are the outward manifestation of excessive and/or hyper-synchronous abnormal electrical activity of neurons in the cerebral cortex of the brain. A seizure often occurs when the electrical activity of the brain becomes more xe2x80x9csynchronizedxe2x80x9d as would be the case when the person is in a drowsy state.
A seizure patient may suffer from any combination of different types of seizures. Grand mal seizures are the most common form of epilepsy and are characterized by convulsions with tonic-clonic contractions of the muscles. Absence seizures (previously referred to as xe2x80x9cpetit malxe2x80x9d) are characterized by a brief and sudden loss of consciousness. The psychomotor form of seizures is characterized by a clouding of consciousness for one or two minutes. A complex partial seizure is characterized by a complete loss of consciousness. The type of seizure experienced is typically dependent upon the function of the portion of the cerebral cortex where hypersynchronous activity is occurring. Many types of seizures generally involve the entire brain, while certain types, such as partial seizures, begin in one part of the brain and may remain local.
Regardless of the type of epilepsy, seizures significantly limit the autonomy of the patient. When hit with a seizure attack, the patient typically loses some level of control of his/her body. In most cases, seizures occur without prior warning to the patient. As a result, epileptic seizures pose a serious safety hazard to the patient as others surrounding the patient. For example, a patient hit with a sudden seizure attack while he/she is driving a car may endanger his/her own safety as well as the safety of others. Seizure patients are also exposed to a risk of bodily harm when operating machinery and even in daily activities such as crossing a street or going down stairs.
Researchers have developed a number of techniques for treating seizure disorders and its symptoms. For example, research has shown that inhibiting (namely, reducing the excitation of neurons) the substantia nigra in the brain increases the threshold for seizure occurrence. Researchers have also found that increasing the activity of neurons in the external Globus Pallidum (GPe) increases inhibition of neurons in the subthalamic nucleus which in turn inhibits neural activity in the substantia nigra. Neurosurgeons have also been able to diminish the symptoms of many neural disorders by lesioning certain brain areas, examples being lesioning the ventral portion of the internal Globus Pallidus and the Vim Thalamus for treating movement disorders. Alternatively, it has been demonstrated that open-loop Deep Brain Stimulation (DBS) at high frequencies (100 Hz or higher) of certain brain structures can alleviate, diminish, or completely stop symptoms of tremor, rigidity, akinesia or hemiballism much like creating a lesion. Electrical stimulation of the nervous system has also been used to suppress seizures. Finally, infusion of certain drugs into a region of the brain can affect the excitability of the neurons at the site of infusion as disclosed in U.S. Pat. No. 5,713,923 (Rise et al.) assigned to Medtronic, Inc.
Others have studied the effects of electrically stimulating the vagus nerve as a means of xe2x80x9cdesynchronizingxe2x80x9d the electrical activity of the brain. It has been observed that stimulation of the vagus nerve with certain parameters caused de-synchronization of the brain""s electrical activity in animal models. These concepts were disclosed by Zabara in U.S. Pat. Nos. 4,867,164 and 5,025,807. De-synchronization can be thought of as xe2x80x9calertingxe2x80x9d phenomena since it reflects active mental activity.
Under another approach, researchers have devised algorithms to detect the onset of a seizure. Qu and Gotman reported a system that recognizes patterns of electrical activity similar to a template developed from recording an actual seizure. See H. Qu and J. Gotman, xe2x80x9cA Seizure Warning System for Long-term Epilepsy Monitoringxe2x80x9d, Neurology, 1995;45:2250-2254. Similarly, Osario et. al. have reported an algorithm applied to signals recorded from intracranial electrodes capable of 100% seizure detection rate with 0% false negatives and minimal false positives. See I. Osario, M. Frei D. Lerner, S. Wilkinson, xe2x80x9cA Method for Accurate Automated Real-time Seizure Detectionxe2x80x9d, Epilepsia, Vol. 36, Suppl. 4, 1995. In each of these techniques for recognizing the onset of a seizure, the developers employ two processes. The first process is to extract certain features from the signals representing the electrical activity of the brain. Examples of the signal features include the signal power or the frequency spectrum of the signals. The second process is to recognize a pattern or set of values for those features which characterize a brain state that will reliably lead to a seizure.
Using these pattern recognition techniques, researchers have developed warning systems to alert the seizure patient of a possible seizure onset. For example, U.S. Pat. Nos. 3,863.625 and 4,566,464 disclose epileptic seizure warning systems producing audio and visual warning signals to the patient prior to the possible onset of a seizure. The warning devices are external devices which can be worn in a shirt pocket of a seizure patient. Such an approach is generally simpler in design than the above-described techniques for treatment of seizures and provides the patient prior warning of a possible seizure onset. Advantageously over the above-mentioned methods, these device allows the patient to take appropriate action to minimize physical injury to the patient and others. This approach, however, requires the patient to constantly carry around the monitoring device causing inconvenience to the patient especially if the monitoring device is misplaced. The use of audio and visual signals as the warning mechanism may also not be as effective if the device is buried underneath a heavy coat or is outside of the hearing range of the patient. In addition, this device is ineffective for seizure patients who have impaired vision or hearing.
The present invention is directed to overcoming the disadvantages of the foregoing systems.
As explained in more detail below, the present invention overcomes the above-noted and other shortcomings of prior techniques for warning of epileptic seizures.
A preferred form of the invention consists of a sensing portion capable of detecting the onset of a seizure, a signal processing portion, and a therapy delivery portion. The sensing portion may be an electrical sensor, chemical sensor, and/or a sensor for sensing physiological changes. The particular structure and parameter to measure may be selected from any known techniques which provide indication of the possible onset of a seizure. The signal processing portion processes and analyzes the sensed signal using an algorithm for recognizing a pattern scheme indicative of the onset of a seizure. If a pattern indicative of the onset of a seizure is recognized, the therapy delivery portion is triggered. The therapy delivery portion is preferably a stimulation electrode which delivers sensory stimulation to the patient thereby alerting the patient of the onset of a seizure.
Sensory stimulation may encompass any combination of touch, sight or sound stimuli. The patient may then take appropriate action to avoid physical injury. For example, if the patient is driving a car when he/she is given a warning signal under the present invention, the patient may immediately stop the car. Further, research has found that the human body is capable of aborting seizures through sensory self stimulation. For example, some patients who have a sensors experience associated with a partial seizure, called an aura, will slap themselves to prevent the generalized seizure that normally follows. Accordingly, under the present invention, if a patient is provided sensory stimulation warning the patient of the possibility of a seizure onset, the patient may take similar action to prevent the seizure. In fact, if the sensory stimulation is sufficiently intense. it may obviate the need for the patient to do anything since the sensory stimulation is equivalent to slapping themselves. Moreover, the cognitive recognition of the possibility of a seizure may in itself serve to abort the occurrence of the seizure. For example, the patient may engage in a mental activity such as performing mathematical computations to xe2x80x9cde-synchronizexe2x80x9d the neurons, thereby reducing the hypersynchronous of the neurons.
Under another embodiment, the invention includes a sensing portion, a signal generating portion and a therapy delivery portion. Under this embodiment, the sensing portion monitors electrical, chemical and/or physiological activity of the patient. The signal generating portion transduces the sensed activity of the patient to a corresponding electrical signal. The therapy delivery portion provides sensory stimulation to the patient based on the electrical signal provided by the signal generating portion. Sensory stimulation may be provided by stimulation of the dorsal column of the spinal cord. Alternatively it may be provided by stimulation of a region of the thalamus or cortex representing a sensory function such as skin sensation or sound, visual or olfactory perception. The patient is thereby provided continuous sensory stimulus relating to electrical, chemical and/or physiological activity of the patient sensed by the sensing portion. Before the patient experiences a seizure, the patient will have sensed a certain pattern of sensory stimulus. After one or more of such seizure episodes, the patient may thereby learn to recognize patterns which are indicative of a seizure onset. By recognizing these patterns, the patient may thereby take appropriate action as discussed herein.
By using the foregoing techniques, seizure disorders, including epilepsy, can be treated and seizures can be alleviated or prevented using sensory stimulation to consciously alert the patient of the onset of a seizure. By alerting the patient of a possible seizure onset, the patient may take action to minimize the risk of injury result from a loss of bodily control. Moreover, mental awareness by the patient of the possibility of a seizure in itself may thereby prevent the seizure from occurring.
Examples of the more important features of this invention have been broadly outlined above in order that the detailed description that follows may be better understood and so that contributions which this invention provides to the art may be better appreciated. There are, of course, additional features of the invention which will be described herein and which will be included within the subject matter of the claims appended hereto.